The present invention disclosed herein relates to an electronic device, and more particularly, to a trans-impedance amplifier including the same.
Typically, an integrated circuit (IC) chip includes a buffer amplifier. The buffer amplifier is provided at the final terminal of the IC, for example, an output terminal. The buffer amplifier is configured to prevent an input impedance of another IC chip from affecting the IC chip, for example, a circuit connected to the final terminal of the IC chip. For example, the buffer amplifier is configured to have low output impedance and high current driving characteristics.
When a buffer amplifier is not provided to the IC chip, voltage drop may occur in the IC chip due to the influence of the another IC chip connected to the final terminal. Accordingly, a signal is not normally delivered to the another IC chip connected to the final terminal and the another IC chip may not perform normal signal processing. Therefore, a buffer amplifier is typically provided to the final terminal of the IC chip.
As an example of the buffer amplifier, suggested are an inverter-type buffer amplifier, an emitter couple logic (ECL)-type buffer amplifier, and a current mode logic (CML)-type buffer amplifier.
The inverter-type buffer amplifier has excellent current driving characteristics. However, since an input impedance and an output impedance of the inverter-type buffer amplifier have high values, the inverter-type buffer amplifier is not suitable for a high-speed operation. Moreover, the inverter-type buffer amplifier consumes a lot of current and it is difficult to apply the inverter-type buffer amplifier to a differential structure.
The ECL-type buffer amplifier has a high linearity and a low output impedance, so that it is advantageous for a high-speed operation. However, the ECL-type buffer amplifier has a low voltage gain. Additionally, when the ECL-type buffer amplifier is manufactured according to a CMOS process, an output signal of the ECL-type buffer amplifier has non-linear characteristics.
The CML-type buffer amplifier has excellent noise attenuation and voltage gain characteristics. However, when a resistor or an inductor is used as a load, the CML-type buffer amplifier increases a design area greatly. Additionally, the CML-type buffer amplifier has poor gain flatness and large voltage drop, so that it cannot raise output voltage.
As an IC chip including a buffer amplifier, there is a trans-impedance amplifier (TIA). The buffer amplifier may be provided at the final terminal of the TIA. The TIA amplifies an optical power signal outputted from a photo diode and delivers it to a limiting amplifier. It is preferred that the TIA delivers a signal with low distortion characteristics without bandwidth limits. However, in order to improve current driving characteristics, if the areas of input transistors in a buffer amplifier of a TIA are designed larger, the bandwidth of the TIA is limited.
An amount of current consumed by a buffer amplifier of a TIA accounts for most of an amount of current consumed by the TIA. Therefore, the feature (for example, change) of an output current of a buffer amplifier affects a chip power of the TIA. For example, the chip power of the TIA may be distorted by the feature (for example, change) of the output current of the buffer amplifier. The chip power of the TIA is provided to other components of the TIA (for example, an input terminal of the TIA). That is, the distortion of the chip power of the TIA may be fed back to the other components of the TIA and due to this, a signal processed by the components of the TIA may be distorted.